Foamed polymer cup and method for making same

ABSTRACT

An improved polystyrene vending machine cup is made by vacuum forming and deep drawing a sheet consisting of a closed cell foam resin core with a nonporous, smooth tough resin skin on both sides of the core. The sheet is formed by extrusion of a hot sheet of foamable thermoplastic resin and quench chilling the surfaces of the sheet to form the skins on each side of the core. The cup can be held in the hand when filled with material having a temperature of 100* C.

Unite States Patent Tiffin et a1. 5] May 30, 1972 [54] FOANED POLYMERCUP AND 2,917,217 12 1959 Sisson ..229 4.5 METHOD FOR MAKING SAL IE3,011,217 12/1951 Carlson.. ....264/53 3,042,972 7/1962 Lafierty....264/53 Inventors: James Tlffin, 710 Colgate Lane, 3,111,710 11/1963Plymale ..264/53 Newark, Del. 19711; Earl Erdman, 117 Carlie Rd.,Lynnfield, Wilmington, Del. FOREIGN PATENTS OR APPLICATIONS 19803854,586 1 H1960 Great Britain ..264/53 [22] Filed: June 7, 1966 OTHERPUBLICATIONS [21] Appl. No.: 555,922

Collins, Controlled Density Foam," in SPE Journal, pp. Related U.S.Applicatio Data 705- 09, July, 1960. [63] Continuation of Ser, No.261,683, Feb. 28, 1963, Fri-many Examiner Robert white abandonedAssistant ExaminerAllen M. Sokal Attorney-Cushman, Darby & Cushman [52]U.S. Cl. ..229/l.5 B, 229/35 R, 264/48,

264/92, 264/321 57 ABSTRACT [51] Int. Cl ..B29c 17/03, B29d 27/00 58Field of Search ..264/92,98,48,51,53; An improved Polystyrene vendingmachine cup is made by 229/15 vacuum forming and deep drawing a sheetconsisting of a closed cell foam resin core with a nonporous, smoothtough 56] References Cited resin skin on both sides of the core. Thesheet is formed by extrusion of a hot sheet of foamable thermoplasticresin and UNITED STATES PATENTS quench chilling the surfaces of thesheet to form the skins on each side of the core. The cup can be held inthe hand when 2,893,877 7/1959 Nickolls ..264/53 X filled with materialhaving a temperature of 00 C 3,039,911 6/1962 Fox .264/92 X 2,905,3509/1951 Edwards ..229/1 6 Claims, 8 Drawing Figures FOAMED POLYMER CUPAND METHOD FOR MAKING SAME The present application is a continuation ofapplication Ser. No. 261,683, filed Feb. 28, 1963 and now abandoned.

The present invention relates to the preparation of containers fromfoamed polystyrene and other thennoplastic resins.

It has been proposed to vacuum form foamed polystyrene and otherthermoplastic resins to prepare cups and other containers, e.g. LaffertyU.S. Pat. No., 3,042,972. There is normally difficulty in vacuum formingfoamed sheets because of the porosity of the product.

It has been proposed in the past to chill an expansible sheet ofthermoplastic resin as it comes out of the extruder. Such chilling isdone prior to the time any substantial expansion or foaming takes placeas in the Lafferty patent above and in Carlson U.S. Pat. No., 3,011,217.When vacuum forming is employed and the expansible material is foameddifficulty is encountered due to the three dimensional nature of theexpanson.

It has also been proposed in Aykanian et al., U.S. Pat. Nos., 2,905,972and 2,945,261, to foam a thermoplastic resin as it emerges from anextruder. The expansion is allowed to continue until the foam contactsinto pressure contact with the surface of a fonning die. The foamprepared in such a manner is of low density, e.g. not over 6 lbs/cu. ft.The Aykanian et al., patents highlight the fact that attempts to preparefoamed thermoplastic resins directly by extrusion means have beenunsuccessful, since when such resins are extruded into air above theirfoaming temperatures, they foam into wrinkled, corrugated structures.Aykanian et al., also indicate that their products are in the finalformed condition and do not indicate that their products can be workedinto other shapes. Carlson U.S. Pat. No., 2,857,625, is similar to theAykanian et al., patents.

It is an object of the present invention to develop a novel method forforming a nonporous, tough skin on foamed thermoplastic resins.

Another object is to obtain a surface on foamed thermoplastic resins, e.g. polystyrene, more mechanically stable in further finishingoperations.

A further object is to prepare cups and other containers from foamedpolystyrene and other foamed thermoplastic resins having a smoother,cleaner, less absorbent surface and an overall better appearance.

An additional object is to prepare wrinkle and distortion free vacuumformed foamed thermoplastic resins.

Another object is to prepare high density foamed sheets of thermoplasticresins, e.g. polystyrene, from which containers can be vacuum formed.

Still further objects and the entire scope of applicability of thepresent invention will become apparent from the detailed descriptiongiven hereinafter; it should be understood, however, that the detaileddescription and specific examples, while indicating preferredembodiments of the invention, are given by way of illustration only,since various changes and modifications within the spirit and scope ofthe invention will become apparent to those skilled in the art from thisdetailed description.

It has now been found that these objects can be attained by forming atough skin on the foamed sheet of thermoplastic resin as it comes out ofthe extruder. The skin is formed by rapid chilling of the surfaces ofthe sheet as it comes out of the extruder while not chilling the majorportion of the sheet whereby it continues to expand to form the foam.

The invention will be understood best in connection with the drawingswherein:

FIG. 1 is a sectional view of an extruder for the foam;

FIG. 2 is a perspective view showing the foam sheet as it comes out ofthe extruder;

FIG. 3 is a somewhat schematic sectional view of a vacuum cup former;

FIG. 4 is a schematic view taken along the line 4-4 of FIG. 2;

FIG. 5 is a schematic view of an alternative chilling device;

FIG. 6 is a sectional view along the line 6-6 of FIG. 2;

FIG. 7 is a vertical elevation of a cup made according to the invention;and

FIG. 8 is a sectional view along the line 7--7 of FIG. 7.

Referring more specifically to FIG. 1 of the drawings, there areprovided pellets of a composition containing 50 parts of the high impactpolystyrene (Foster Grant's Tuflex 216, polystyrene modified with 5percent polybutadiene) and 50 parts of regular crystal polystyrene(Koppers Dylene 8). This composition is called hereinafter CompositionA.

90 parts of Composition A were tumbled for 5 to 10 minutes with 10 partsof Dow Pelespan 101 (expansible polystyrene beads containing 6 percentpentane) and 0.5 part of Bayol 35 (a petroleum aliphatic hydrocarbonwhite oil). The tumbling was carried out at room temperature. There werethen added 0.3 part of powdered anhydrous citric acid and 0.4 parts ofpowdered sodium bicarbonate and the mixture tumbled for an additional 15to 20 minutes. The resulting mixture 2 was added to the hopper zone 4 ofa conventional plastic extruder 6. The hopper zone had a temperature of225 F. The plastic mixture then passed into the barrel 8 of the extruderwhere it was softened and kneaded within the barrel with the aid ofscrew 10. The temperature within the barrel was 325-350 F. The pressurewithin the barrel as measured at the discharge end was 2,500 psi and thetemperature at the adapter was 340 F. The plastic then entered die 14and was extruded through land aperture or slot opening 16 to form afoamed polystyrene sheet 18. The sheet has a temperature of about 300 F.as it emerges from the extruder. It remains dense for about 0.5 inchbefore it starts to expand or swell. When expansion occurs it does so inall three dimensions. The sheet as it emerges from the slot 16 has athickness of 35 mils. Within a fraction of an inch of the slot 16 thetop surface 20 of the sheet 18 is rapidly chilled by means of mixed airand water blasts 24 from pressure mixer 26 via nozzle 27 whilesimultaneously the bottom surface 22 of the sheet 18 is rapidly chilledby mixed air and water blasts 28 from pressure mixer 30 via nozzle 32 asshown in FIG. 4. Alternatively the air and water can be applied throughseparate nozzles, an alternative modification is shown in FIG. 5 whereinno water is employed but instead air 34 is blasted through nozzles 36upon the upper surface 20 and air 38 is blasted through nozzles 40 uponlower surface 22. In place of air other inert gases can be used, e.g.nitrogen, argon, carbon dioxide, helium, etc. The air was blasted at 50feet/sec. at room temperature (70 F The exact temperature and velocityof the air and/or water chillant is not critical. The critical featureis that the polystyrene (or other thermoplastic resin) surface be cooledrapidly below its yield point so that essentially no bubbles form on thesurfaces of the sheet while the inside of the sheet retains sufficientheat to foam well. The air temperature and velocity are controlled so asto cool just the skin, i.e. about 3 to 15 percent at the top of thesheet and about 3 to 15 percent at the bottom of the sheet while notcooling the remainder of the sheet so that the majority of the sheetwill still foam. If the cooling is too great, then the sheet will notexpand at all. Those skilled in the art, however, can readily controlthe chilling so that it is neither too little or too great. In thespecific example the sheet after the chilling expanded to a totalthickness of about 90 mils. The top skin 20 and bottom skin 22 were each5 mils thick and the core 25 was about mils thick.

The chilling produced a top skin and bottom skin which weresubstantially bubble free and smooth and produced containers having agood appearance, and having good insulating properties. The products,e.g. cups were less absorbent than products made from conventionalfoamed polystyrene sheets.

The chilling treatment also prevented wrinkling and distortion of thefoamed polystyrene sheet and gave a smoother, cleaner surface which wasmore mechanically resistant during the requisite further finishingoperations. Consequently, it was easier to work with the sheet. Thefoamed sheet having the top and bottom skins had a density of 25 lbs/cu.ft.

The invention is particularly adapted to making high density foamedsheets, e.g. 18-45 lbs/cu. ft. and preferably 20-35 lbs/cu. ft.

The sheet as it comes from the extruder must be at least 5 mils thickand generally is -45 mils. The foamed sheet is usually 60-120 milsthick, preferably 85-90 mils, although the sheet can be as thick as 300mils. Each skin is usually 5-10 mils thick. Since the outer skins areessentially unexpanded they are of considerably higher density than thefoamed core, e.g. they can have a density of 60-66 lbs./cu.ft.

The temperature within the extruder can be varied in conventionalmanner, e.g. it is preferably between 270 and 340 F. althoughtemperatures up to 450 F. can be employed. The pressure in the extruderat the adapter is usually LOGO-4,000 psi and the pressure in the die ofthe extruder about SOD-1,500 psi when using polystyrene. In the specificexample the pressure in the die was 1,000 psi and in the barrel it was2,500 psi.

The foamed sheet 18 as shown schematically in FIG. 3, was heated untilpliable and then was passed over vacuum former 42 where it was deepdrawn to form a cup and then allowed to cool. The vacuum former includesa male member or plug 46 and a female die 48 having vacuum lines 50therein. The vacuum drawing can be carried out in any conventionalfashion, e.g. as shown in Caine application, Ser. No. 176,148 filed Feb.27, 1962 as a division of application, Ser. No. 711,739, Jan. 28, 1958,now U.S. Pat. No. 3,045,887. The extruded sheet of polystyrene having afoamed core and integral top and bottom unfoamed skins can be formed inthe same manner as regular unfoamed polystyrene. In the thermo formingthe three layer sheet is stretched to form the cup. The stretchingreduces the thickness of the sheet, e.g. from 85-90 mils to 25-40 milsat the center of the cup. This thickness can be varied from 10-50 milswhile still retaining the ability to be used as a hot drink containerwhile at the same time not being unduly bulky.

The cup 44 is made up of an integral three layer unit consisting of anunfoamed outer skin 52, a foamed core 54 and an unfoamed inner skin 56.In the vacuum forming the relative thickness of the three layers is notaltered materially. It is to be understood that some areas of the cupare not stretched as much as others. Thus the thickness under the lip 58can be as high as 60 mils while the mid portion of the cup is -40 milsthick. The bottom of the cup also is usually thicker than the midportion. The lip can be formed in any convenient manner either as abead, a flange or otherwise.

Cups formed by the present process having a thickness of as little as 10mils or as high as or 50 mils, had an insulating value sufficient thateven when they contained boiling water, aqueous coffee, aqueous tea oraqueous chocolate, they could be held comfortably in the hand. Incontrast conventional hot drink cups of lower density foams havethickness of 80 mils or over. Thus the present cups are nestable invending machines and elsewhere in a lesser space than conventionalfoamed cups.

For best resultings a nucleating agent should be used in forming thefoamed composition, as described in Erdman application, Ser. No. 244,382filed Dec. 13, 1962. The entire disclosure of the Erdman application ishereby incorporated by reference.

Thus there can be used a composition containing 50-95 percent ofnonfoaming polystyrene, e.g. regular polystyrene and/or high impactpolystyrene and 5-50 percent expansible polystyrene. When a nucleatingagent is employed it is used in an amount of from 0.02 to 10 percent ofthe total polystyrene by weight. Preferably 0.4 to 2 percent of thenucleating agent is used.

conventionally nucleating agents made up of two materials which react toform carbon dioxide and water can be used. The two materials arenormally used in approximately equivalent amounts. As the carbon dioxideliberating materials there can be used ammonium, alkali and alkalineearth carbonates or bicarbonates, e.g. ammonium bicarbonate, sodiumbicarbonate, sodium carbonate, potassium bicarbonate or calciumcarbonate. The other material is an acid or acid reacting salt,preferably solid, which is sufficiently strong to liberate the carbondioxide from the carbonate or bicarbonate.

Generally the acid has at least 3.0 milliequivalents of acidic hydrogenand preferably at least 10.0 milliequivalents, per gram. The acid can beorganic or inorganic. Suitable acidic materials include boric acid,sodium dihydrogen phosphate, fumaric acid, malonic acid, oxalic acid,citric acid, tartaric acid, potassium acid tartrate chloroacetic acid,maleic acid, succinic acid, phthalic acid. In place of the anhydrousacids or salts there can be used the solid hydrates, e.g. oxalic aciddihydrate and citric acid monohydrate.

Suitable foaming agents for the thermoplastic resins are well known andthe selection of the particular foaming agent to be employed is dictatedprimarily by the particular thermoplastic resin in which it is to beincorporated. The preferred foaming agents are nonreactive liquids whichhave not more than a slight solvent action on the thermoplastic resinand which volatilize below the softening point of the thermoplasticresin. Usually the resin, e.g. expansible polystyrene contains 1 to 15percent of a volatile liquid, preferably 4.5 to 9 percent by weight. Theliquid preferably boils below 100 C. Typical examples of suitablefoaming agents include aliphatic hydrocarbons boiling between 10 and 100C. and preferably between 30 and C., e.g. petroleum ether (containingprimarily pentane or hexane or a mixture of these hydrocarbons),pentane, hexane, isopentane, heptane, cyclohexane, cyclopentane,pentadiene, and neopentane. Other volatile liquids include methanol,ethanol, methyl acetate, ethyl acetate, acetone, methyl formate, ethylfor-mate, dichloroethylene, isopropyl chloride, propionaldehyde,diisopropyl ether, trichlorofluoromethane, a mixture of pentane with5-30 percent of a lower halogenated hydrocarbon such as methylenechloride.

While not essential there can also be added a wetting agent such asBayol 35, kerosene having an average of at least eight carbon atoms inthe molecule, alkylphenol-alkylene oxide adducts, e.g. Triton X-lOO(t-octylphenol-ethylene oxide adduct having 10 ethylene oxide units inthe molecule), sodium lauryl sulfate and sodium dodecylbenzenesulfonate. The wetting agents can be nonionic or anionic.

The foams prepared normally have closed cells of uniform size, usuallywith a cell diameter of from 0.01 to 0.5 mm.

When employing polystyrene there can be employed normal crystal gradepolystyrene or high impact polystyrene or a mixture containing 5 topercent normal crystal grade polystyrene and the balance high impactpolystyrene. When employing a thermoplastic styrene polymer it normallycontains greater that 50 percent by weight of styrene and preferably atleast 70 percent by weight of styrene in its structure. High impactpolystyrenes are frequently prepared by polymerizing monomeric styrenein the presence of 2% to 10 percent by weight of a rubbery diene polymeror by polymerizing styrene in the presence of such amounts of adifunctional material. Examples of high impact styrenes include aterpolymer of 5 percent acrylonitrile, 5 percent butadiene and 90percent styrene; a copolymer of 5 percent butadiene and 95 percentstyrene; the product made by polymerizing 95 percent of styrene in thepresence of 5 percent of polybutadiene; a copolymer of 5 percentchlorosulfonated polyethylene and 95 percent styrene; a blend of 97.5percent polystyrene and 2.5 percent polybutadiene; a blend of 95 percentpolystyrene and 5 percent of hydrogenated polybutadiene containing 35.4percent residual unsaturation; polystyrene formed in the presence of 5percent hydrogenated polybutadiene containing 4.5 percent of residualunsaturation; a blend of a 5 percent polystyrene and 5 percentpolyisoprene, and a copolymer of 99.5 percent styrene and 0.5 percentdivinyl benzene.

Unless other wise indicated all parts and percentages are by weight.

The foamable thermoplastic resins which can be extruded according to theinvention include cellulose ethers and esters, e.g. ethyl cellulose,cellulose acetate, cellulose acetate-butyrate, homopolymers andinterpolymers of monomeric compounds containing the grouping such asolefins, e.g. ethylene, propylene, isobutylene, vinyl halides, e.g.vinyl chloride; vinylidene chloride; vinyl esters of carboxylic acids;e.g. vinyl acetate; vinyl stearate, vinyl benzoate; vinyl ethers, e.g.vinyl methyl ether; vinyl ethyl ether, vinyl isobutyl ether; unsaturatedcarboxylic acids and derivatives thereof, e.g. acrylic acid, methacrylicacid, methyl acrylate, ethyl acrylate, methyl methacrylate, acrylamide,acrylonitrile, methacrylonitrile, and interpolymers of the abovementioned vinylidene monomers with alpha, beta-unsaturatedpolycarboxylic acids and derivatives thereof, e.g. maleic anhydride,diethyl maleate, dibutyl fumarate, diallyl maleate, dipropyl maleate,etc. A preferred class of materials with which optimum results areobtained are rigid, relatively nonelastic thermoplastic resins such ashomopolymers of vinylrdene aromatic hydrocarbons and ring halogenatedderivatives thereof, e.g. styrene, o-chlorostyrene, p-chlorostyrene,2,5-dichlorostyrene, 2,4-dichlorostyrene, p-methylstyrene,pethylstyrene, alpha-methylstyrene, vinyl naphthylene and interpolymersof such vinylidene monomers with each other and with other vinylidenemonomers in which the interpolymer contains at least 70 percent of thevinylidene aromatic hydrocarbon compound, e.g. a copolymer of 70 percentstyrene and 30 percent acrylonitrile. As previously indicated the mostpreferred resins are thermoplastic styrene polymers containing at least70 percent by weight styrene in the structures.

Other suitable thermoplastic resins include polycarbonates, e.g. thepolymer from bisphenol A and diphenyl carbonate; polyurethanes, e.g.from toluene diisocyanate and polypropylene glycol molecular weight2025; Dacron (polyethylene terephthalate), nylon (e.g. polymerichexamethylene adipamide).

While the invention is of particular importance in the manufacture ofcups it is also useful in preparing other open containers such as foodtrays, buckets, plates and other foamed articles, e.g. face masks. Thecontainers can be used to package cheese, ice cream or other foodstuff.

The articles are preferably made by vacuum drawing the foamedthermoplastic resin sheet. The invention is particularly valuable invacuum drawing because of the elimination of the troubles normallyencountered in vacuum forming porous sheets.

The term integrally united" as used herein means a direct union of theinner core with the outer skins without the use of an adhesive or otherintermediate material,

The three layer sheet after foaming of the core can be vacuum formedimmediately or it can be stored, e.g. in roll form and subsequentlyheated to a temperature sufficient to permit vacuum forming.

We claim:

1. A process of thermoforming a closed cell thermoplastic styrene resinfoam sheet into a seamless cup, said sheet being wrinkle and distortionfree and having a thickness of 60 to 120 mils and a density between 18and 45 lbs/cu. ft. and consisting of l a closed cell foam resin core,(2) a nonporous, smooth, tough resin outer skin on one side of the core,and (3) a nonporous, smooth, tough resin skin on the other side of thecore, said core comprising over 50 percent of the total thickness ofsaid skins and core, said core being integral with said skins and beingcomposed of the identical material as said skins, said skins having asubstantially higher density than said core and each skin being at least3 percent of the total thickness of the skins and core, said sheethaving been formed by extrusion of a hot sheet of foamable thermoplasticresin and quench chilling the surfaces of said sheet to form said skinson each side of said core, said process comprising supplying sufiicientheat to thermoform said sheet and thermoforming said sheet by vacuumforming and deep drawing into a cup having wall means and a core densityof 18 to 45 lbs/cu. ft., a major portion of said cup wall means having athickness between 10 and 50 mils., said cup being characterized by beingcapable of being held in the hand when filled with material having atemperature of 100 C. and being nestable in v endin machines in a lesserspace than lower density foams, said wal means being in stretchedcondition.

2. A process according to claim 1 wherein the sheet prior to vacuumforming has a thickness of -90 mils and a density of 20-35 lbs/cu. ft.and the core is at least 70 percent of the total thickness of the coreand skins and the major portion of the cup wall means has a thicknessbetween 25 and 40 mils.

3. A process according to claim 2 wherein the starting foamed sheet isone which has been foamed with the aid of a nucleating agent and theclosed cells have a cell diameter of 0.01 to 0.5 mm.

4. A process according to claim 1 wherein the deep drawing is to anextent sufiicient to reduce the thickness of the sheet to at least aboutone-half its original thickness in the major portion of the cup wallmeans.

5. A cup made by the process of claim 1.

6. A cup having wall means, said cup having been made by a processcomprising forming a foam sheet by extrusion of a hot, wrinkle anddistortion free sheet of foamable thermoplastic styrene polymer having athickness of 85 to mils and a density of 35 lbs./cu.ft. and quenchchilling the surfaces of said sheet to form a sheet consisting of l) aclosed cell foam resin core, (2) a nonporous, smooth, tough resin outerskin on one side of the core, and (3) a nonporous, smooth, tough resinskin on the other side of the core, said core comprising over 50 percentof the total thickness of said skins and core, said core being integralwith said skins and being composed of the identical material as saidskins, said skins having a substantially higher density than said coreand each skin being at least 3 percent of the total thickness of theskins and core, and supplying sufficient heat to thermoform said sheetand thermoforming said sheet into a cup having a core density of 12 to45 lbs./cu.ft., said wall means being in stretched condition.

2. A process according to claim 1 wherein the sheet prior to vacuumforming has a thickness of 85-90 mils and a density of 20-35 lbs./cu.ft. and the core is at least 70 percent of the total thickness of thecore and skins and the major portion of the cup wall means has athickness between 25 and 40 mils.
 3. A process according to claim 2wherein the starting foamed sheet is one which has been foamed with theaid of a nucleating agent and the closed cells have a cell diameter of0.01 to 0.5 mm.
 4. A proCess according to claim 1 wherein the deepdrawing is to an extent sufficient to reduce the thickness of the sheetto at least about one-half its original thickness in the major portionof the cup wall means.
 5. A cup made by the process of claim
 1. 6. A cuphaving wall means, said cup having been made by a process comprisingforming a foam sheet by extrusion of a hot, wrinkle and distortion freesheet of foamable thermoplastic styrene polymer having a thickness of 85to 90 mils and a density of 35 lbs./cu.ft. and quench chilling thesurfaces of said sheet to form a sheet consisting of (1) a closed cellfoam resin core, (2) a nonporous, smooth, tough resin outer skin on oneside of the core, and (3) a nonporous, smooth, tough resin skin on theother side of the core, said core comprising over 50 percent of thetotal thickness of said skins and core, said core being integral withsaid skins and being composed of the identical material as said skins,said skins having a substantially higher density than said core and eachskin being at least 3 percent of the total thickness of the skins andcore, and supplying sufficient heat to thermoform said sheet andthermoforming said sheet into a cup having a core density of 12 to 45lbs./cu.ft., said wall means being in stretched condition.